We are continuing our study on the nature of transcription termination in E. coli and of the mechanism of action of the bacteriophage lambda N-protein, which suppresses transcription termination. The synthesis and function of the lambda cII-protein is under investigation. Synthesis of pcII is regulated at a post-transcriptional level by the E. coli himA-hip gene products. We are constructing two new vector systems. The first of these is designed to clone DNA fragments bearing promoters active in E. coli. The second, a shuttle vector, is tailored for the cloning of large, and/or unstable DNA fragments, as well as for the reconstitution of genes from overlapping DNA clones. We are examining the ability of coliphage Pl to stimulate the precise excision of transposons. The responsible gene has been subcloned, and we are attempting to clarify the molecular mechanism of this reaction.